Multi-combination vehicles commonly referred to as “road-trains” have been in use for some time, particularly in Australia, for the purpose of hauling freight such as mining ores, or other commodities, over aboveground and even underground roadways. Known road-trains typically include a powered primary load-carrying vehicle such as a wheeled, rigid body truck and one or more load-carrying towed vehicles. The towed vehicle may include a wheeled dolly and a semi-trailer coupled to the dolly. Both the towing and towed vehicles may include load-carrying bodies of the side-tipping type.
In remote areas, it is not unusual for road-trains to include a plurality of trailers. However, even though truck engines of up to a thousand horsepower have been developed, the transmission systems and especially the gearboxes are unable to tolerate large payloads and therefore limit the total payload of a road-train. In addition, when such road-trains have been used in underground mines, there is a lack of traction on larger inclines leading to such road-trains only being able to navigate relatively small inclines.
Due to this problem, powered trailers have been developed by the present applicant and which are the subjects of separate patent applications. These powered trailers in brief rely on an engine on a trailer that provides the additional horsepower and traction for the road-train to carry more payload, consequently saving on operational costs.
However, when the road-train has delivered its load and is being returned empty to collect more payload, it is preferable for the powered trailer to be simply towed. Such a scenario may be warranted where, for example, one is using a dedicated road-train to transport ore from a mine to a processing plant that may be hundreds of kilometers away. Being towed may conserve fuel but may lead to transmission and engine wear and damage. This is because in a powered trailer road-train, even though the engine of the power trailer is not running, the drive wheels still cause the drive train of the powered trailer and hence its gearbox to be rotated. This is undesirable for without the engine running the engine oil pump is not running leading to a lack of lubrication. This not only can damage the transmission and the engine but also any superchargers or turbochargers, these being common accessories in diesel engines.
The inventor is not aware of any known powered trailer drive train where the drive train or the wheel rotation may be disengaged from the gearbox and the engine so that even when the vehicle or trailer wheels are turning the operator has the choice to decouple the engine and transmission.
Most drive trains require a separate oil pump that circulates the oil required for lubrication and heat dispersion for the drive train assembly. Generally this is a pump that is driven by the input shaft. It therefore follows that if the input shaft is decoupled from the drive wheels, when the powered trailer is towed and its engine is not running the oil pump for the drive train assembly is not working even though components of the drive train assembly are still being rotated. This can lead to obvious failure of and damage to the drive train components. The present invention also provides for an embodiment where this problem is overcome.
The oil pump assembly assists in ensuring that the drive train assembly remains lubricated even when the power trailer engine is not running. However, since the gear box has a separate lubrication system, the oil pump assembly does not imply that the decoupling of the drive train is an option when the engine is not running. It is to be clearly understood that when the engine is not running, the drive train assembly must be decoupled regardless of the presence of a separate lubrication system for the drive train assembly. Whether an oil pump assembly is provided also depends on where the decoupling of the drive train assembly occurs. If it occurs within the drive train assembly then additional lubrication is still required. However if it occurs at the wheel hubs then the additional lubrication is not essential.